The present invention relates to the extrusion of metals. In this respect, U.S. Pat. No. 3,872,703 to Green teaches rotary metal extrusion through the use of a shoe and groove apparatus. That is, the surface of a rotatable cylindrical wheel or drum has a groove whose dimensions are approximately the same as the external dimensions of the material to be extruded. Operating in conjunction with this groove is a fixed shoe member positioned above the groove to form an elongated passageway between the shoe and the drum. At one end of the shoe a die-carrying abutment member projects into and closes off the passageway.
As extrusion material is fed into the open end of the elongated passageway, three of its sides are gripped by the groove and the fourth side abuts the shoe. The friction generated by the three sides of the groove is greater than the total friction generated on the single side by the shoe. Hence, the rotation of the drum draws the extrusion material through the passageway to the abutment member, and places the extrusion material under such internal pressure that its yield point is exceeded. In this manner the extrusion material is extruded through the die and drawn off.
Major difficulties experienced in prior devices, however, are binding of the shoe on the drum and the production of excess amounts of flash, flash being extrusion material that passes through clearance spaces between the shoe and the drum. Binding has occured either when too much flash escaped or when attempts were made to reduce clearance spaces between the shoe and the drum.
Attempts have been made to eliminate or reduce flash by extending the shoe member into the passageway a small amount. See, for example, the Green patent mentioned above. While such attempts may keep the amount of flash from increasing if the shoe member moves away from the drum, they still allow flash to pass between the sides of the shoe's inwardly projecting portion and the sides of the groove. This flash is undesirable because, aside from being wasted metal, it can accumulate between the shoe and the drum and cause them to bind. Therefore, it is an object of the present invention to provide an improved continuous rotary metal extrusion apparatus such that excess flash is reduced to an acceptable level and the shoe does not tend to bind on the drum.